This invention relates to fire detection systems and more particularly to a two stage detection circuit for conserving energy in a battery-operated fire detection system or the like.
The prior art contains many different types of fire detection, fire alarm, and fire-extinguishing systems. Many of these systems run on AC power and many others utilize AC power which is converted into rectified DC power used to operate the detection elements, the alarm-initiating devices, and/or the fire-extinguishing discharge or release.
Many areas exist where no AC power is available such as in remote wilderness cabins, motor vehices of all types, shipping enclosures or containers, and the like. Similarly, many applications exist wherein battery-powered systems may be used a back-ups where power may be interrupted for long periods of time such as in buildings, warehouses, factories and the like, particularly those facilities located in areas subject to prolonged power failures. In all of such circumstances, a reliable, battery-operated fire detection system is required.
The prior art has devised many such battery-operated fire detection systems, or battery-operated systems for detecting various other types of alarm conditions. But, in nearly all such systems, the batteries are relatively short-lived since power must be continually applied to the detection system and continually available to discharge or release the fire-extinguishing fluid or transmit the alarm signal. Some systems utilize relatively expensive, sophisticated battery systems but these are not generally feasible for widespread commercial use.
Additionally, all such systems waste a tremendous amount of electrical energy since the detection system and the alarm activation system or fire-extinguishing release system associated therewith represent a significant and continuous drain on the system. All of this energy is wasted and, should the battery become drained, the fire detection system could fail if a fire developed after the battery became dead or too weak to supply the necessary energy.
A few systems have been developed which utilize detection elements which do not require a separate source of power, but these devices have generally proved to be too sensitive and unreliable for accurate use. Most of these systems will not meet Underwriters Laboratory standards and are subject to frequent false alarms and/or to the expensive, erroneous and sometimes embarrassing release or discharge of fire-extinguishing fluids under false alarm conditions. Additionally, while some of the detectors can operate without a separate source of power, the means for discharging the fire-extinguishing system or for transmitting some type of alarm signal is severely limited unless it also is supplied with a separate battery or source of power.
In summary, the prior art systems either employ relatively reliable battery-powered detectors which cause a continuous drain on the battery thereby shortening its life, and wasting power; or they are relatively unreliable, overly-sensitive and subject to false alarms and expensive erroneous discharges.
The double detection circuit of the present invention solves all of the problems of the prior art and avoids all of its short-comings by providing a highly reliable, battery-operated detection system which does not represent a continuous drain on the battery but which is only activated after an initial or primary fire-indicative condition has been detected by a relatively sensitive, passive detection element.